BGP for outbound load balancing

[kjanakiraman]

I am running BGP between two routers. On router A the ethernet interface has the ip address x.x.x.x1 and on the router B the ethernet interface is having ip address y.y.y.y1. These two interface is connected to a switch and from the switch the connection goes to a Software based firewall running on windows. In the firewall i am doing PAT and load balancing by pating certain internal subnet with x.x.x.x2 and certain internal subnet to y.y.y.y2. (The firewall will have two public NIC cards with one representing Router A Network and the other Router B Network

Now If Router A fails or the link goes down will all my traffic goes out using router B? By BGP if Router A goes down the Router B will carry the Network of Router A. Then all the local subnet which is pated with x.x.x.2(Router A) will go automatically via Router B?

Can some on advice or suggest if this will work and if not any automatic routing can be done?

Thanks in Advance

[paddyxdoyle]

Hi,

Are you connecting to seperate ISPs? have a look through the following document which contains some good examples of load sharing using BGP using a single ISP and multiple ISPs:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf3

HTH

Paddy

[kjanakiraman]

Thanks for the mail. I am running BGP with two different ISP on two different Router. I would like to know if i PAT certain internal subnet through ISP A and Certain internal subnet throuhg ISP B and if ISP A goes down will the traffic PATed to ISP A will go out throuhg ISP B?

Thanks in Advance

[vcjones]

If I am interpreting your configuration question correctly the answer is "NO." This assumes:

You are assigned a different set of IP addresses by each ISP and are NOT multihomed using BGP. You will have no problems sending your traffic PATted to ISP A out via ISP B, however, that traffic has a "return address" using an IP serviced by ISP A, and any packets being sent back by the other end of the connection will be routed through the Internet to ISP A for delivery and ISP A will discard them because the link between you and ISP A is down.

If you firewall is smart enough to adjust the PAT on the fly to use the correct IP range for the link being used, all connections will break when the ISP is swapped, but your inside users will be able to continue working by refreshing their connections (such as by hitting the reload button on their web browser). How tolerable this will be will, of course, depend on the applications and how often either ISP fails. Note that the disruption will also recur when ISP A returns to operation and the traffic routed via ISP B due to the failure again gets routed via ISP A.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

[kjanakiraman]

Thanks for your reply. I am using multi-homing with BGP configured in the routers. In this case will it work?

Thanks in Advance

[vcjones]

As long as you are NAT/PATting to IP source addresses which are in your public IP range, then everything should work. The whole idea of BGP multihoming is that your IP addresses are independent of the ISP used to reach them. The challenge with NAT/PAT is that once a translation is set up, it must remain static until it is no longer needed, otherwise, the connectivity supported by that translation will fail.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

[kjanakiraman]

Thanks for your information. I will check for the same and revert back if i face any problem.